Helium isotopes provide no evidence for deep mantle involvement in widespread Cenozoic volcanism across Central Asia

Barry, T.L.; Ivanov, A.V.; Rasskazov, S.V.; Demonterova, E.I.; Dunai, T.J.; Davies, G.R.; Harrison, D.. 2007 Helium isotopes provide no evidence for deep mantle involvement in widespread Cenozoic volcanism across Central Asia. Lithos, 95 (3-4). 415-424.

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Small-volume alkali basaltic volcanism has occurred intermittently for the past + 30 My across a vast area of thick continental crust from southern Siberia, through Mongolia to northeast China. With a lack of evidence for Basin-and-Range-type crustal extension or rifting, models to explain the widely dispersed, yet long-lived, volcanism tend to favour involvement of one or more mantle plume(s). We examine the range of 3He/4He isotope values in olivine phenocrysts from basalts, and their entrained mantle xenoliths, from Hamar Daban in southern Siberia, and Hangai in central Mongolia, in order to examine whether upwelling lower mantle appears to be present beneath central Asia and thus test the validity of the plume model for this region. Our results show that the maximum 3He/4He value for the Siberian basalts is 8.12 ± 0.2Ra, and the maximum value for Mongolian basalts is 9.5 ± 0.5Ra. These values suggest that there is no significant contribution from a high 3He/4He primordial component that would strongly argue a lower mantle source. Overlap with commonly reported values for MORB leads us to propose that the source of the magmatism derives from the shallow asthenosphere. Alternative models to a deeply sourced mantle plume that may be able to explain the magmatism include: a shallow thermal anomaly confined to the upper mantle but either fed laterally or caused by thermal blanketing of the large Asian landmass; replacement or delamination of the lowermost lithosphere in response to tectonic stresses; or large-scale mantle disturbance or overturn caused by a protracted history of subduction beneath central Asia that ended regionally with the Jurassic closure of the Mongol-Okhotsk Ocean, but continues further afield with the present Indo-Asia collision.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: BGS Programmes > NERC Isotope Geoscience Laboratory
ISSN: 0024-4937
Additional Information. Not used in RCUK Gateway to Research.: Acknowledgements TLB wishes to thank the NERC (Studentship GT4/95/155/E) and the Royal Society (Study Visit Grant Number 16005). Many thanks to B. Windley for initiating the helium isotope study, and L. Coogan and M. Branney for useful comments on the manuscript. Comments by D. Ionov on an earlier version of this manuscript helped to greatly improve the arguments presented here. R. Thompson and an anonymous reviewer are also thanked for their comments. Study of AVI has been supported by RFBR projects 05-05-64477 and 05-05-97260_Baikal. AVI and EID also thank the Russian Scientific Support Foundation and Grant 1588-2006.5 of the President of Russian Federation for personal and financial support. Markova M.E. and Lozhkin V.I. helped with ICP-MS analyses of Siberian samples.
Additional Keywords: Cenozoic, Volcanism, Helium, Mantle dynamics, Asia - Central
NORA Subject Terms: Earth Sciences
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Date made live: 16 Sep 2008 15:50 +0 (UTC)

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